Mitigating Cache Side-channel Attacks via Fast Flushing Mechanism

Objective With the rising demand for secure computing, cache-based side-channel attacks have become a critical threat to modern processors. Conventional data cache designs do not account for information leakage caused by malicious memory access patterns, enabling adversaries to infer sensitive data from subtle variations in cache access latency. Existing countermeasures, such as cache mapping randomization and cache flushing, provide partial protection but incur considerable hardware overhead and performance degradation, particularly in resource-constrained private caches such as L1 and L2. To address this limitation, this study focuses on L1 data caches and proposes a fast flushing mechanism based on Time-To-Live (TTL) control. The method mitigates side-channel leakage while minimizing additional hardware complexity and performance cost. Methods This study proposes a fast cache flushing method that introduces a lightweight 3-bit TTL field into each cache line, together with a global time register (Time), to enable efficient cache invalidation. When a flush instruction is issued, the Time register is incremented, and all cache lines are checked against their TTL values. Only lines that remain valid and contain modified data are invalidated and written back, thereby reducing flushing overhead. To ensure robustness and correctness, several auxiliary strategies are incorporated, including mechanisms to handle TTL wraparound, preserve data consistency, and strengthen resistance against advanced side-channel attacks. The proposed mechanism is realized through custom instruction set extensions on an RISC-V processor platform. Results and Discussions The proposed cache flushing mechanism exhibits significant performance benefits in representative application scenarios. Experimental evaluation shows that it reduces average flushing latency by approximately 70% relative to conventional flushing techniques. In side-channel security tests based on the Prime+Probe attack model, an adversary probing 1024 cache lines after the victim executes a flush operation is unable to recover valid sensitive information patterns, thereby confirming the security effectiveness of the proposed architecture. Regarding hardware overhead, the design introduces only about 8% additional logic and approximately 0.01% extra storage cost for TTL fields compared with conventional cache structures. Conclusions This paper presents a fast cache flushing mechanism to defend against cache-based side-channel attacks. The proposed method achieves a balanced trade-off between security and performance. Experimental results show that it substantially reduces cache flushing latency while effectively mitigating typical side-channel threats. The design is particularly suited for deployment in resource-constrained private caches such as L1 and L2. Hardware implementation further confirms the lightweight nature and engineering feasibility of the approach, indicating strong potential for practical application.